Pelvis and Perineum 1.2 Flashcards
What type of muscles are the muscles of the male perineum?
skeletal
What are the muscles in the male perineum innervated by?
by the pudendal nerve and its branches
What do most of the muscles of the male perineum have attachments to?
central tendon of the perineum (perineal body)
What is the perineal body in men?
a midline structure located just anterior to the anal canal and just behind the bulb of the penis
What is the subdivision of the perineum?
- Anterior urogenital triangle
2. Posterior anal triangle
How are the two triangles divided?
imaginary horizontal line connecting the 2 ischial tuberosities divides the perineum into these 2 descriptive triangles
What do the ischiocavernosus and bulbospongiosus muscles cover
- crus of the penis (corpus cavernosum) and the bulb of the penis (corpus spongiosum)
- these bodies are the erectile tissue of the penis
What does contraction of the bulbospongiosus muscle help?
helps to evacuate any remaining urine in the spongy urethra
Where does the external urethral sphincter muscle arise from?
ischiopubic ramus
Where does the external urethral sphincter muscle insert?
into a median raphe and the perineal body and extends superoanteriorly along the prostate to the neck of the urinary bladder
What is the action of the external urethral sphincter muscle?
acting together, the urethral sphincter muscles on both sides form a sphincter that compresses the membranous portion of the male urethra
What is the innervation of the external urethral sphincter muscle?
perineal branch of the pudendal nerve (S2-S4)
What forms a true sphincter of the urthera (external urethral sphincter) in men?
only a portion of the muscle
What does another portion of the muscle form?
- extends vertically to the bladder and invests the prostatic urethra anteriorly and laterally
- unknown how or whether this muscle acts on the prostatic urethra.
What is at the neck of the male urinary bladder?
an internal urethral sphincter
How is the internal urethral sphincter innervated?
smooth muscle, sympathetically innervated from L1-L2
Why is the internal urethral sphincter important during ejaculation?
it prevents semen from entering the urinary bladder or urine from entering the prostatic urethra
What is erectile dysfunction?
an inability to achieve and/or maintain penile erection sufficient for sexual intercourse
What does sexual stimulation normally release?
- nitric oxide from nerve endings and vascular endothelial cells
- thus relaxing the smooth muscle tone and increasing blood flow
- which then compresses the veins draining the erectile tissues
- allows for engorgement of the tissues
What do drugs that treat ed aid?
relaxation of the smooth muscle
What does the external anal sphincter surround?
the last 2 cm of the anal canal
What does the external anal sphincter consist of?
consists of subcutaneous, superficial, and deep portions
What are the attachments of the external anal sphincter?
- Some fibers attach anteriorly to the perineal body and posteriorly to the anococcygeal ligament
- Fibers also may join the superficial transverse perineal, the levator ani, and the bulbospongiosus muscles
- Deep fibers interlace with the puborectalis muscle.
What is the action of the external anal sphincter?
- muscle is in a tonic state of contraction and has no antagonist
- keeps the anal canal closed
What is the innervation of the external anal sphincter?
inferior rectal branches (largely S4) of the pudendal nerve (S2-S4)
Where is the internal sphincter?
lies deep to the external anal sphincter (that is, just superior to the external anal sphincter)
What is the control of the internal anal sphincter?
smooth muscle sphincter involuntary control
What type of fibres maintain its tonic contraction?
sympathetic
What do parasympathetic fibers do?
- relax muscle tone and permit expansion of the anal canal during defecation or flatulence
- this action also requires that the external anal sphincter be relaxed simultaneously
What can trauma to the anal mucosal lining (e.g. from compacted faeces) lead to?
anal infection that can spread into the adjacent sphincter muscles and beyond, into the ischioanal fossae of the fat-filled anal triangle
What is the female pelvic viscera innervated largely by?
lower portion of the parasympathetic division of the autonomic nervous system
How do these parasympathetic preganglionic fibres arise?
as the pelvic splanchnic nerves from the nerve roots of S2, S3, and S4
Where do many of these preganglionic parasympathetic fibres synapse?
in the inferior hypogastric (pelvic) plexus, adjacent to the rectum, uterus, ovary, and uterine tubes
Where does postganglionic parasympathetic from the inferior hypogastric plexus course?
to the respective pelvic viscera
What do pain afferents from ovaries, uterine tubes and fundus and body of uterus follow?
sympathetic fibers back to the spinal cord (T11 or T12 to L1-L2 levels)
How do pain fibers from the uterine cervix and vagina (subperitoneal structures) travel back to the spinal cord?
via the pelvic splanchnic nerves (S2-S4)
Where do cell bodies for these pain afferents reside?
in the spinal (dorsal root) ganglia of the respective spinal cord levels
Where is pain from the pelvic and perineal viscera is felt over?
the dermatome areas T11-L2 and S2-S4; it is largely confined to the hypogastric region, pelvis, and perineum and occasionally radiates into the upper part of the lower limb
What does the pudendal (somatic) nerve innervate? (W)
skin and skeletal muscle of the female perineum and external genitalia
Where does the pudendal nerve arise from? (W)
anterior rami of S2, S3, and S4 spinal cord levels
What does the pundeal nerve do after emerging from the pudendal (Alcock’s) canal? (W)
- divides into inferior anal (rectal) nerves
1. the perineal nerve
2. the dorsal nerve of the clitoris
Where do parasympathetic fibers arise from? (W)
S2-S4 levels
Where do the parasympathetic fibres travel? (W)
travel in pelvic splanchnic nerves to the inferior hypogastric plexus and uterovaginal plexus
What do the parasympathetic fibres stimulate in the women?
- vaginal secretions
- erection of the clitoris
- engorgement of the bulbs of the vestibule (vasodilation of the arteries supplying the erectile tissue of the crus of the clitoris, clitoris, and vestibular bulb)
How do you achieve local anaesthesia of the perineal area?
- pudendal nerve may be blocked selectively
- by infiltrating a local anesthetic into the region of the pudendal canal
- thus numbing the S2-S4 somatic region (skin and skeletal muscle) of the perineum
